A procedure for the purification of communal and/or industrial waste water involves firstly passing the water into a collecting tank or vessel in which the water is subjected to preliminary settlement or clarification, followed then by a conventional biological purifying stage. A biological purifying stage of that kind comprises for example an activated sludge installation to which air or oxygen is fed. In accordance with the partial pressure in the air, the water becomes enriched with oxygen and, in the course of time, micro-organisms establish themselves at the interface formed by the solid substances with water and air. Those micro-organisms interact with substances which are dissolved and also dispersed in the waste water. After the biological purification stage, the water is then passed into a post-settlement or post-clarification vessel with a sludge remover.
It will be apparent from the foregoing that conventional installations for the purification of waste waters involve a high level of apparatus expenditure and take up a great deal of space, while operation thereof, and the maintenance that they involve, gives rise to a not inconsiderable level of expenditure, including from the point of view of personnel.
Not least an improvement in the level of efficiency of such installations requires a feed of pure oxygen, which still further increases the costs involved while in addition the oxygen which is employed in that situation is often only utilised to an inadequate degree.